1. Field
The present invention relates to controlling the operation of a communication device in a system where transmissions between a communication device and an access node occur on one or a plurality of carriers. In one embodiment, each carrier is a block of orthogonal sub-carriers.
2. Description of the Related Art
A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various service applications.
A communication system is a facility which facilitates the communication between two or more entities such as the communication devices, network entities and other nodes. A communication system may be provided by one or more interconnect networks. One or more gateway nodes may be provided for interconnecting various networks of the system. For example, a gateway node is typically provided between an access network and other communication networks, for example a core network and/or a data network.
An appropriate access system allows the communication device to access to the wider communication system. An access to the wider communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Communication systems providing wireless access typically enable at least some mobility for the users thereof. Examples of these include wireless communications systems where the access is provided by means of an arrangement of cellular access networks. Other examples of wireless access technologies include different wireless local area networks (WLANs) and satellite based communication systems. A wireless access system typically operates in accordance with a wireless standard and/or with a set of specifications which set out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched bearer or a packet switched bearer, or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner in which communication should be implemented between the user equipment and the elements of the networks and their functions and responsibilities are typically defined by a predefined communication protocol. Such protocols and or parameters further define the frequency spectrum to be used by which part of the communications system, the transmission power to be used etc.
In the cellular systems a network entity in the form of a base station provides a node for communication with mobile devices in one or more cells or sectors. It is noted that in certain systems a base station is called ‘Node B’. Typically the operation of a base station apparatus and other apparatus of an access system required for the communication is controlled by a particular control entity. The control entity is typically interconnected with other control entities of the particular communication network. Examples of cellular access systems include, in order of their evolution, GSM (Global System for Mobile) EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN), Universal Terrestrial Radio Access Networks (UTRAN) and evolved UTRAN (EUTRAN).
In the Long Term Evolution (LTE) System Release 8, downlink transmissions are made according to an orthogonal frequency division multiple access (OFDMA) technique, and uplink transmissions are made according to a single carrier frequency division multiple access (SCFDMA) technique. Each transmission is made using a group of orthogonal sub-carriers. Sub-carriers are grouped into units called resource blocks, and a user device can make or receive transmissions using groups of resource blocks ranging up to a predetermined maximum number of resource blocks within a predetermined frequency block called a carrier. The bandwidth available for transmissions between a device and a radio access network node generally comprises a plurality of carriers; and each transmission is made on a selected one of the carriers. A further development of LTE Release 8 (which development is known as LTE-Advanced) provides for carrier aggregation, where two or more carriers are aggregated in order to support transmission bandwidths wider than that defined by a single carrier. In summary, devices operating under LTE Release 8 are served by a single carrier, whereas devices operating under LTE-Advanced can receive or transmit simultaneously on a plurality of carriers. The Medium Access Control layer (MAC layer) generates respective transport blocks for each scheduled carrier, and all possible HARQ repeat transmissions for any transport block take place on the same carrier to which the respective transport block was mapped.
For each carrier, some time resources (OFDM Symbols) are reserved for at least one of the transmission of physical downlink control channels (Physical Downlink Control Channel—PDCCH), and other time resources (OFDM symbols) are reserved for the transmission of physical downlink shared channels (Physical Downlink Control Channel—PDSCH), and also uplink in the case of Time Division Duplexing (TDD). The physical control channels (PDCCH) carry scheduling assignments and other control information. The physical shared channels are physical channels for which the physical downlink control channels carry scheduling information. A communication device may receive scheduling assignment(s) for a PDSCH on one carrier via a PDCCH on a different carrier. This is known as cross carrier scheduling.
It may be that a communication device needs to monitor more than one carrier to check for physical control channels directed to it.
Requiring a communication device to monitor and measure all carriers for possible allocation it is not desirable from the point of view of saving battery power. One technique for saving battery power is the Discontinuous Reception (DRX) technique of the kind specified at section 5.7 of 3GPP TS 36.321 V.9.0.0 (2009-09), in which a communication device is allowed to monitor for PDCCH discontinuously. One proposal is for a communication device to apply the same DRX operation to all carriers. Another proposal aimed at further limiting the energy a communication device expends in checking for PDCCH is to, in accordance with variations in traffic load, provide the communication device with information about which of the plurality of carriers it should monitor for any PDCCH directed to it.